Any tips that I can rely on to almost guarantee getting to 400ft plus?

I have been able to steamroll to about 400/450 from time to time but I died due to stupidity. I once tried hitting a giant the first time I encountered one and you could imagine how that went. On another occasion I was very unlucky because I had 450ft cleared and was on my way to 500 (this was recently, it was about my third of fourth time there ever and my first time I was actually ready for it and not driven down stairs or a chasm) but I walked into a room of shadows which I forgot were there, I was too stupid and panicky to use my staffs of light (yes plural, I had like 2 or 3) and I ended up dying

EDIT: I know Giants are extremely vunerable to poisin, also I slew a unique (an Easterling) I encountered for the first time on that run which felt good

Also to clarify I mainly use high evasion and melee characters, I have a little bit of success with archery.

There are better placed people than me to comment, but since nobody seems to be doing so...

Early survival can require a little luck; it's all about getting a certain critical mass of protection and evasion together to survive initial encounters with the enemy. A strategy that's been quite good for me is early Hardiness on a Fingolfin, pumping Evasion about twice as much as Melee for the first few floors. Just took a character like that down to 400 to see what I put into stats compared to your last couple of posts, and his defence block currently reads [13, 5-14] - that's with Evasion 11, Melee 6. I haven't really invested in much besides Precision and Hardiness so far.

You need to know when the current deficiencies in your equipment are going to make a fight hard to win. The Fingolfin doesn't have a shield so far, so I've been largely avoiding getting sucked into prolonged battles with archers. Having a bow and arrows makes fighting crebain and gorcrow less dangerous. In general if you're underequipped it's better to avoid fights until you're in better shape.

Two-handed weapons are usually clearly superior when you have no shield. I found Narsil this run but kept using the 3d6 greatsword I picked up earlier - it was just so much more damage it would have been silly not to.

Don't think in terms of clearing levels. Stairs are places to retreat to. I just came back from 400 after encountering Othrod; he was a little out of depth, and was outdamaging me enough that it was clear I wasn't going to win. I drank a Murky Brown Potion and retreated to the stairs. Try to have a retreat plan if possible. Enemies that move exactly as fast as you do are enemies you can retreat from without being hit.

In terms of immediate tactics: fight as few enemies as you can at a time. Fighting two enemies in a corridor is better than fighting many enemies in the open. If you have one enemy on one side and three on another, kill the one first, because then you're only fighting the three one-on-one.

Something I haven't tried but I theorise might be helpful - when tweaking Sil-Q, I lowered enemy perception by a couple of points in early levels, and people have been saying it's much easier to survive the start of the game. The same effect could be achieved in Sil by spending 300 XP on Stealth at the start.

Finally, if you check out http://angband.live, you'll find other players there you can ask questions of and can play a game with them there watching and commenting on things you could do to improve.

There's a guide debo posted ages back that was tooled to get you to 400'. Worked by focusing on an artistry start so you could get non-shit items to smooth you past the early game RNG. Getting past 400' is a different matter, as you've found, as that's where orcs taper off and you actually find a variety of threats. Personally, I enjoy running evasion/riposte guys myself, and I just ran another (right now) getting to 600' before saving and coming here, so here goes:

Take the 3-3-5-3 elf who has Will specilization.
I take 4 pts in smithing, just to forge-id the 'junk' jewelery items. I won't invest any more unless the opporunity to create a feanorn lantern presents itself.
I stick to leather armour, round shields, etc.
Play as normal, 2 pts each in Will and Perception, literally everything else into melee/evasion. No purchased skills.
At 400-450', trying to fight 1:1 in corriders might no longer cut it, so it's time to pick up your 'schtik'. I personally love ZoC, so I'll get Finesse/ZoC with Flanking as my bare minimum. This turns combat on it's head, as you're now more effective in open spaces than you are in corridors, at least v hoards. The AI will order the mooks to walk past you if they have friends, in order to cut you off and get flanking bonus'. This can net you 2-3 free attacks per turn, while instead of fighting you keep tyring to 'slide' around the edges of the pack, getting Flanking attacks, and they won't attack en masse but continually try to reposition, giving you more free hits. Eventually the moral breaks and you win/murder them all. Opportunist rounds this off, but costs 3600 and so comes second.
After that just go back into melee/evasion, with the occasional Will skill purchase for emergency utility/resists etc.
Enjoy dying to new and exciting threats at 600'+!

N.B. Giants are most weak to evasion-style builds, as long as you have enough hp to take two hits you should be able to just walk strait up to him and facetank. They swing at +6.

Just ran a simple Fingolfin down to 400' mostly by just putting everything in melee/evasion. I started with clarity which is a luxury, but the will means you get a little less bother with wraiths, melwips etc. & murky potions won't stun if you need to heal in an emergency. Took hardiness when it got close to the cost for an extra evasion.

So some sort of straight melee/evasion build is easiest, if you're still getting caught something is going wrong in your tactics.

Re: Giants - these aren't too bad as long as you don't get caught without space to back out. They are pretty inaccurate with the boulders, as long as you can take a lucky hit you can back away & gain space/time while they miss. Back away from them while you still have the hps for another blow. Heal up or run or kite them with a bow.

Re: whispering shadows - unless you get them before they start spreading close of all the doors to that area. Abandon the loot, area or level if you have to.

I actually had a run yesterday where I got to 400ft with only one near death incident besides the one where I actually died. Basically I ran into that vault that is a bit of a maze and straight inside was a wight that hit me like a truck, a warg, an orc warrior and Orcobal himself flooded out before I could get away. I'll post a dunp later. In regard to the shadows that is what I did, I just forgot they were there and ran into them.

In regard to the shadows that is what I did, I just forgot they were there and ran into them.

As long as you have more than 1 light your light radius will shrink just before you are right on top of them. It's a good idea to start watching for this as much worse things are going to hide in the dark later on.

One trick I sometimes use if I'm lucky enough to find final rest is to use the glow like a radar to detect & hunt them down before they spread. This is easier with an inventory window where it will still glow if it's in your pack. Oh & don't barrel in to a grave wight by mistake, there's a depth range where you will see both around.

Finesse, Dodging->Flanking, Zone of Control, Lorekeeper->Loremaster, in that order. don't train anything but melee/evasion until you get 7 perception. Try to make sure you have an escape route if you stumble unexpectedly on an orc pack or something along those lines. One reason it's good to have dodging, flanking, and ZoC is that you can fight in open areas against a few enemies, which allows you to have a line of escape should the fight suddenly turn bad. Finally, don't be afraid to bail on a floor at such an early depth - it's incredibly unlikely that you're going to miss an artifact of any value, and it's not worth dying to whispering shadows. Do try to kill those as fast as you can though - it's good to carry a final rest weapon around for this purpose, and can make inner light, keen senses, or song of the trees (my pref) useful around that depth.

Edit: Try to play an easy character too. I suggest 2543 w/ Feanor or 2444 with Finarfin.